ST. PETERSBURG — Before a crowd of about 250 people in his hometown of St. Petersburg, Charlie Crist declared his candidacy as a Democrat to return next year to the governor’s office he held as a Republican from 2007 through 2010.

Crist told the crowd of mostly Democrats, but a smattering of Republicans, that he wants to represent the middle class and small businesses. He said that under incumbent Republican Gov. Rick Scott, “big business, big contributors, big lobbyists, they’re the winner.”

“My record is pretty clear,” he said, “putting the people first.”

The event began with endorsements from some big Democratic names, including U.S. Rep. Kathy Castor of Tampa and former Attorney General Bob Butterworth.

Crist also got backing from former state Rep. Rick Kriseman, who faces the voters today in his own race for mayor of St. Petersburg.

In his speech, Crist emphasized actions he took as governor that fit with Democratic principles, including restoration of felon rights, extending early voting hours in 2008 at a time when Republicans feared the move would help candidate Barack Oabama, and using federal economic stimulus money he said prevented layoffs of 20,000 public school teachers.

He made several pledges:

* To renew the effort to create high-speed rail and mass transit in Florida.

* To restore what he said were billions of dollars in cuts by Gov. Rick Scott to K-12 public schools and higher education, including the Bright Futures college tuition aid program.

* A new effort to make it easier for homeowners to use solar power and “end the monopoly of big utility companies.”

* An “expansive new program” providing tuition aid to graduate students in medicine, science, math and technology if they remain in Florida after school.

Crist repeatedly accused Scott of “corporate giveaways” to campaign donors and selling out to special interests.

In Tallahassee, he said, “Government of the people has been replaced by cronyism and government on the fringes. The voice of the people has been silenced by the financial bullies and the special interests. ... You really have no advocate there any more.”

Crist said Scott’s economic policy – sure to be the centerpiece of Scott’s campaign – is “entirely focused on giving money away to big corporations” and “flying around Florida in a private jet to hold press conferences.”

Crist promised instead to “spend money to grow the economy from the middle class out.”

“It’s going to be a long year and a tough fight,” Crist said. An ad being aired by Scott’s independent political committee, Let’s Get To Work, uses past quotes from Democrats, including Alex Sink of Tampa, Al Gore and Tampa Mayor Bob Buckhorn, bashing Crist as an untrustworthy flip-flopper and political opportunist.

The committee wouldn’t say how much it’s spending on the initial ad buy; Politico reported it was $525,000, not a large buy for Florida.

But Let’s Get to Work has raised more than $18 million in 2012-13 so far, and Democrats have seized on comments by Scott that he intends to spend up to $25 million “defining my opponent” even before the election year starts.

Meanwhile, the state Republican Party held a news conference call with reporters in which George LeMieux, formerly Crist’s political right-hand man, called Crist’s political reversal “breathtaking.”

LeMieux was Crist’s campaign manager and chief of staff in the attorney general’s office and governor’s office. Crist later appointed LeMieux to a vacant U.S. Senate seat, but LeMieux failed to win the Republican primary to hold the seat.

“This is the largest change of positions by a leading American political figure in as quick a period of time as we’ve had in American history,” LeMieux said, referring to Crist’s switch from Republican to no-party in 2010, and to Democrat last year.

“He’s changed positions so much he’s unrecognizable now.”

Florida Republicans, bitter over what they regard as Crist’s betrayal, have been blasting him in news releases and speeches for more than a year, with their latest anti-Crist slogan being “Unfit to govern.’’ The ad marks their upgrading the attacks to broadcast.

Crist has replied repeatedly to such criticism that while some of his own political views have changed, it was the GOP that changed more, becoming dominated by tea party conservatives. “The party left me,” he contends.

The crowd at Crist’s announcement including a broad sampling of local and state Democratic politicos, including state Reps. Mark Danish of Tampa and Dwight Dudley and Darryl Rouson of St. Petersburg; former state Sen. Dan Gelber of Miami; Tampa City Council member Charlie Miranda and more.

“Notwithstanding labels, he’s always stood up for Floridians and hasn’t been afraid to stand up to his former party,” Castor said in an interview. She told the crowd that Crist, unlike Scott, acted aggressively against the BP oil company after the disastrous 2010 oil spill.

Asked whether Crist, who no longer has the huge Republican fundraising base of his 2006 race for governor, can defeat Scott’s projected $100 million campaign, Butterworth responded, “If anyone can, he can.”

Gelber added, “People know him and like him, and they know Rick Scott and don’t like him.”

Kriseman told the crowd, “To make all of Florida better, we must start by making Charlie Crist’s hometown better,” a reference to his election for mayor today against incumbent Bill Foster.

Asked if he was taking a political risk by choosing sides in a partisan race when he faces a nonpartisan election Tuesday, Kriseman said, “It’s all about what’s best for our community — a governor who understands St. Petersburg. There are Republicans who are going to be supportive of Charlie Crist.”